The present invention relates to a method for manufacturing a piezoelectric element provided with a thin and flat fired piezoelectric body with no warpage.
Recently, there has been desired a displacement control device capable of adjusting the optical path length and position in submicrometer in the fields of optics, precision machinery, semiconductor manufacturing, etc. In response to this, there is proceeding development of piezoelectric devices such as a piezoelectric actuator utilizing strain (displacement, change in shape) based on the reverse piezoelectric effect caused upon applying an electric field to a piezoelectric body and a piezoelectric sensor utilizing charge generation (polarization) caused upon applying stress to a piezoelectric body on the basis of a piezoelectric effect.
The core of these piezoelectric devices is a piezoelectric element obtained by putting a piezoelectric body between electrodes. Of these, the piezoelectric body can be manufactured by forming a piezoelectric material into a film shape by a thin film method and firing it at high temperature (hereinbelow, a piezoelectric body obtained in this way is referred to as a fired piezoelectric body). Since, in the fired piezoelectric body, the direction of intrinsic polarization (bias of charge) is not oriented if the fired piezoelectric body is left as it is, almost no strain is generated, and it cannot be used as a piezoelectric element.
Therefore, in a manufacturing process of a piezoelectric element formed by putting a fired piezoelectric body between electrodes, the piezoelectric element is generally subjected to a polarization treatment. The polarization treatment is generally performed just before the final step of cleaning or the like. The target of the polarization treatment is naturally the fired piezoelectric body constituting the piezoelectric element. The polarization treatment is generally performed by applying a voltage of several kV/mm for about several tens of minutes in the atmosphere or in a liquid. In the polarized fired piezoelectric body (piezoelectric element), the direction of the intrinsic polarization is oriented to almost the same direction and is not reposited to have a polarization value (remnant polarization) even without applying any voltage. Then, a voltage is applied to this (an electric field is applied), strain (displacement, deformation) is generated on the basis of the amount of the voltage.